Generally, unlike a primary battery, research into a rechargeable secondary battery has actively progressed with the development of high-tech fields such as a digital camera, a cellular phone, a notebook computer, a hybrid car, or the like. An example of a secondary battery may include a nickel-cadmium battery, a nickel-metal hydride battery, a nickel-hydrogen battery, and a lithium secondary battery. Among others, the lithium secondary battery operated at a voltage of 3.6V or more is used as a power supply for portable electronic devices or is used for a high-output hybrid car by connecting several lithium secondary batteries in series. The lithium secondary battery has an operating voltage three times or more than that of the nickel-cadmium battery or the nickel-metal hydride battery and has excellent energy density per unit weight, such that the use thereof has been rapidly increased.
The lithium secondary battery may be manufactured in various types. An example of a representative type may include a cylinder type and a prismatic type that are mainly used for the lithium ion battery. A lithium polymer battery, which has been recently spotlighted, is manufactured in a pouched type having flexibility, such that the shape of the lithium polymer battery is relatively free. In addition, the lithium polymer battery is light while having excellent stability, such that it is advantageous in slimness and lightness of a portable electronic device.
FIG. 1 shows a structure of a pouched type lithium secondary battery according to the related art. A pouched type lithium secondary battery 50 according to the related art is configured to include a battery unit 51 and a case 10 providing a space 11 in which the battery unit 51 is received.
The battery unit 51 has a shape where an anode plate, a separator, and a cathode plate are sequentially disposed to be wound in one direction or a plurality of sheets of anode plates, separators, and a plurality of sheets of cathode plates are stacked. Each electrode plate of the battery unit 51 is electrically connected to anode and cathode tabs 52a and 52b. Ends of the anode and cathode tabs 52a and 52b are protruded to the outside through a sealing surface 12 of the case 10. Ends of the protruded anode and cathode tabs 52a and 52b are connected to terminals of a protective circuit board (not shown).
The outer surfaces of the anode and cathode tabs 52a and 52b are each wound with a sealing tape 13 in order to prevent an electrical short between the case 10 and the electrode tabs 52a and 52b at a portion where they contact the sealing surface 12. Unlike a cylinder type or a prismatic type can structure of which the thick film is molded into a metal material, the case 10 is a pouched type case having an intermediate layer formed of a metal foil and inner and outer skin layers formed of an insulation film that are attached to both surfaces of the metal foil. The pouched type case has excellent formability and can be freely bent. As described above, the case 10 is provided with a space 11 in which the battery unit 51 can be received and the sealing surface 12 provided on a surface that is hot-melted along the edge of the space 11. FIG. 2 is a diagram showing a cross section taken along A-A of FIG. 1. The case 10 is a composite film that is configured to include an intermediate layer formed of a metal foil, i.e., an aluminum foil and an inner skin layer and an outer skin layer attached to an inner surface and an outer surface of the intermediate layer and formed of an insulation film to protect the intermediate layer.
The space 11 formed in the case 10 receives the battery unit 51 disposed in an order of an anode plate 51a, a separator 51c, and a cathode plate 51b. An anode tab 52a and a cathode tab 52b are drawn out from the anode and cathode plates 51a and 51b. The ends of the drawn electrode tabs 52a and 52b may be exposed to the outside through the sealing surface 12 of the case 10 and the sealing tape 13 is wound on the outer surfaces of the electrode tabs 52a and 52b at the sealing surface 12.
In the pouched type lithium secondary battery 50 having the above structure, the battery unit 51 is completed by electrically connecting the anode and cathode tabs 52a and 52b to the anode plates 51a and the cathode plate 51b and then, winding the anode plate 51a, the separator 51c, and the cathode plate 51b in one direction in the state where they are sequentially disposed. The completed battery unit 51 is mounted in the case 10 formed with the space 11 through a drawing process and ends of each electrode tabs 52a and 52b are exposed to the outside of the case 10 when being mounted. In this state, the pouched type lithium secondary battery 50 is completed by hot-melting the sealing surface 12 of the case 10 by applying predetermined heat and pressure thereto. Whether the completed pouched type lithium secondary battery 50 is abnormal is determined by a series of formation process such as charging, aging, discharging, etc., in order to stabilize the battery structure.
In this connection, Korean Laid-Open Patent Publication No. 2005-000594 discloses a method of casing a pouched type lithium secondary battery. The pouched type lithium secondary battery of the above document has a structure capable of easily detecting a difference in open loop voltage due to a short-circuit occurring when the cathode tab contacts the metal layer of the case, since the inner skin layer of the case is broken due to the application of the same positive potential to the metal layer of the case and the anode tab.
Meanwhile, when the high-output lithium battery such as the hybrid car, etc., is required, the pouches shown in FIGS. 1 and 2 is stacked several tens to several hundreds and are connected in series in order to obtain high voltage.
Since the pouched type lithium polymer battery is formed of a soft aluminum pouch that may be easily warped or bent, it should be protected with a solid case device to be used over a long period of time. However, the related art used a scheme of connecting the anode tabs and the cathode tabs of each pouch by a printed circuit board (PCB) formed with circuit patterns for connecting the pouches in series and receiving them in the case.
However, according to the method of configuring the high-output lithium battery by stacking the lithium polymer pouch according to the related art, the lithium polymer pouch having a soft structure may not be completely protected and the scheme of stacking the pouches several times and connecting them by the PCB is also incomplete, such that the high-output lithium battery is not strong to the change in environment such as external impacts, etc. A need exists for a method capable of more firmly and stably stacking the pouch units configuring the lithium battery used as the high-output power supply and reliably connecting the pouch units in series and parallel.